FED-STD-791 Lubricants, Liquid Fuels, And Related Products, Testing Method OfThis test method standard is composed of standard test methods for sampling, inspecting and testing lubricants, liquid fuels and related products. It is issued pursuant to the Federal Property and Administration Services Act of 1949, as amended and its application to the purchase of commodities referred to herein is mandatory on all Federal agencies.

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'�NOTE:This draft dated 15 April 2006' by DasH - Page 154 of 460

FED-STD-791D

decanting is possible. If the material is a liquid at the conclusion of the 30-minute centrifuging

period, or if it cannot be compacted, stopper the centrifuge tube and replace it in storage for an

additional 30 days. At the end of the second storage period, proceed as directed in 6.12.

6.14 Place the centrifuge tube in an upright position in an oven controlled at 104� "

2.5�C (220� "5�F) for approximately 2 h.

6.15 Remove the centrifuge tube from the oven and place it in a desiccator to cool to

room temperature. Weigh the tube and contents to the nearest mg. Subtract the weight of the

empty centrifuge tube to determine the weight of the separated material.

NOTE 4:

If the residue remains a liquid at the end of the second 30-day storage period,

centrifuge the tube as specified in 6.12. Remove the tube from the centrifuge and

note the volume of the separated liquids to the nearest 0.05 mL.

7. CALCULATIONS

7.1 Calculate the percent incompatibility for each test, using the following formulas:

Theoretica l zero incompatib ility = R + T

Evidence of incompatib ility = X - (R + T)

X - (R + T)

Percent incompatibility =

* 100

0.9 (50 r + 50 t)

where:

R = weight of separated material in reference oil (g/50 mL of oil). See 6.2.

T = weight of separated material in sample oil (g/50 mL) of oil). See 6.2

X = weight of separated material found in compatibility test. See 6.15.

r = weight percent of additive in reference oil. This information is supplied by the Test

Monitoring Center. See 5.6

t = weight percent additive in sample oil. This information is supplied by the manufacturer

of the sample oil.

0.9 = assumed specific gravity of both reference oil and sample.

7.2 Calculate and report incompatibility for each reference oil as an average of the two

test values obtained for the reference oil.

NOTE 5:

It may be of interest to make a chemical analysis of the residue found in the

incompatible oil mixture.

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